Thermocouple signals are typically in the millivolt or even microvolt range, and thermocouples inherently usually have a relatively high impedance. Both factors, the low signal levels and the high source impedance, lead to signals from the thermocouples being very susceptible to noise. In addition, particularly in a medical scenario such as an ablation procedure, where thermocouples may be used for critical measurements on patients, it is important that noise from thermocouples is reduced and that the signals derived from the thermocouples give true temperature readings. Methods for compensating or reducing noise levels from thermocouples, and for ensuring that the signals are valid, are known in the art.
For example, U.S. Pat. No. 6,402,742, to Blewett, et al., whose disclosure is incorporated herein by reference, describes a temperature measuring circuit which is coupled to the prostate and urethral thermocouples. The disclosure also describes a controller which operates from AC line voltage that is filtered to reduce noise.
U.S. Pat. No. 8,644,523, to Clemow, whose disclosure is incorporated herein by reference, describes a digital circuit arrangement for an ambient noise-reduction system. The arrangement converts analog signals into N-bit digital signals at a sample rate and then subjects the converted signals to digital filtering.
U.S. Pat. No. 9,226,791, to McCarthy et al., whose disclosure is incorporated herein by reference, describes an interface module which may include an input/output (I/O) port that receives digital thermocouple signals from an integrated catheter tip. The digital signals are provided by an analog-to-digital converter.
Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that, to the extent that any terms are defined in these incorporated documents in a manner that conflicts with definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.